A primer on the network Dennis Couture Director

A primer on the network Dennis Couture Director – Rural Markets coutured@nortel. com Congressional staff briefing June 7, 2005

The Telecommunications Network > Our telecommunications network allows us to transmit “information” electronically virtually anywhere. > “Information” takes many forms, each with different characteristics • • • Voice Email Broadcast video Real-time video Gaming Mixing traffic requires solid engineering 2

Traffic types and characteristics Bandwidth Voice Low Delay Tolerance Low Error Tolerance Medium Email Low / Medium High Zero Broadcast video High Medium Real-time video Medium / High Low Medium Gaming Low / Medium Low The more stringent the demands, the more expensive the network is to build and to maintain. 3

What is voice? > Voice is audible human communication • Content is concentrated at frequencies below 1 KHz • Nuance and voice uniqueness reside above 1 KHz • Traditional telephony transmits a maximum of 4 KHz (NOT Hi-Fi) > Other characteristics of voice: • Voice communication is usually half duplex (“wasteful”) • Voice is sensitive to delay • Echo • Delayed “half duplex” speech (“Over to you, Bill!) • Voice is tolerant of interference • The human ear/brain combination is a great receiver • Analog noise is filtered out and ignored • Digital bit errors have virtually no impact on intelligibility 4

Sound Waves 5

A real speech signal 6

Analog Telephony • • Electrical signal mirrors the voice signal Objective is to accurately transport this signal 4 KHz signal allows speaker recognition Common impairments include: – Loss A – Noise – Distortion – Delay • Impairments can accumulate 7 t

Digital Telephony > Analog signal is “sampled” • 8, 000 samples of 8 bits every second • 64 Kbps required to carry normal voice > Samples are transmitted digitally > Signal is reconstructed by connecting the dots > Impairments are minimized • Loss • Noise • Distortion • Delay A > Impairments do not accumulate At this point, the voice has become a stream of data!!! 8 t

Digital Formats > This 64 Kb format is called Pulse Code Modulation (PCM) • 64 Kb is a slow bit rate > Multiple 64 Kb channels can be combined • • This is called Time Domain Multiplexing (TDM) Typically 24 channels are sequenced in a 1. 544 Mb signal These are called DS-1 or T-1 circuits Think of loading a conveyor belt into pre-assigned slots > Multiple DS-1 channels can then be combined • DS-3 carries 28 DS-1 channels or 672 voice channels • Optical systems go much higher • OC-192 carries 129, 024 voice channels 9

Let’s talk about transport > Transmission facilities carry communications from point to point • Access facilities reach out to end users • Interoffice facilities (trunks) connect internal parts of the network > A tremendous amount of telephone company investment lies in transport (much more than switching) • Procurement and installation of cable facilities • Terminal equipment at each end of the facility • Ongoing maintenance costs > These facilities deliver high bandwidths in a reasonably secure manner 10

Fiber Transmission 11

Fiber Optics > Light is pulsed on and off very rapidly • Think naval flashing lights!!! > Fiber optic systems provide: • Very high capacity • FASTER - Bit rates are very high • LONGER - Distance between repeaters is increasing • WIDER - Multiple “colors” can ride on the same fiber • Secure transmission • Excellent reliability • Excellent economics Fiber optic systems carry the vast majority of long distance voice and data traffic 12

Increasing optical bandwidth with Wave Division Multiplexing (WDM) TDM WDM Exploits Higher Speed Similar to Adding Lanes Up to 72 “colors” of light share the same fiber capable of 9, 289, 728 simultaneous calls! 13

Add more lanes to the highway • DWDM Upgrade (Dense Wave Division Multiplexing) • Supports OC-48 and/or 192 line rates • Provides “effective” line rates of Terabits per second. Channel 1 Optical Fiber Channel 2 DWDM Channel 3 Channel n 14 Coupler

Enough of the preliminaries…. . How does the network? 15

Network topology > The network architecture physically resembles a highway or train system • It consists of network nodes (cities and towns) interconnected with transport facilities (roads or tracks) 16

A SONET Network in the D. C. area Synchronous Optical NETwork Looks a lot like the highway system!!! 17

Meanwhile at the edge of the network…. . 18

Telephone Loops Twisted Pairs > Loops connect your telephone to the network > Analog transmission > Long loops (> 18 Kft. ) deteriorate the signal • Loss, Frequency Distortion, Noise > Load coils can correct this distortion • Cut off high frequencies • Preclude use of DSL A Increasing loop length ^ 4 Khz 19 f

Carrier Serving Areas > Short loops (no load coils) are now standard • Less costly to build and maintain • Allows higher frequencies, so as to carry data • DSL can be provisioned in a CSA > High speed links connect the Digital Loop Carrier (DLC) to the central office • May be copper or fiber fed Local Serving Area Central Office DLC 20 Carrier Serving Areas

Mixed Service Delivery With a typical DLC > No Vo. IP in this picture $$ > Common facilities to the remote unit • Mixed TDM and IP traffic > Loop carries analog voice plus IP > Could add Broadband Voice via the PC or an IP Phone > Analog phone service survives power outages Today’s investment supports future services. IP DSLAM IP TDM GR-303 TDM Switch PSTN 21 NG DLC Analog Voice RTP/IP TCP/IP

Mixed Service Delivery With BBDLC and a TDM switch > > > Common facilities to the remote unit carry only IP traffic Loop carries analog voice plus IP BBDLC converts analog voice to IP Could add Broadband Voice via the PC or an IP Phone Analog phone service survives power outages IP RTP/IP IP Gateway IP 22 TCP/IP BB DLC TDM Switch PSTN DSL Vo. IP MGCP MEGACO/H. 248 Analog Voice

Triple Play > Why do Triple Play? ? • One method of extracting more revenue from a DSL line • • > A significant defensive move against the cable threat Triple play is a big step • • • > Content acquisition is an important issue Own or share a head end? Buildout of access network can be costly Impact of HDTV must be considered • • > Trying to improve a marginal business case for Internet Access Bandwidth requirements / channel capacity MPEG-4 equipment Video on Demand is a significant revenue opportunity The demand for more advanced video-related capabilities will continue to rise. 23

Ah, but where do the roads go? > Roads interconnect towns and cities > Access facilities connect users to their local central office > Trunk facilities connect central offices to each other 24

Switching Systems > A digital switch: • Converts voice into a digital format • Interprets the dialed digits • Routes the call to its destination by: • Completing local calls • Transferring all other calls to another switch for completion Central Office Trunks Central Office DLC 25

North American Numbering Plan 26

Numbering Issues > In the wireline world, an area code defines a geographic area • Mobile phones and some Vo. IP services break this model • This is the source of the E 911 problem for both Vo. IP and cellular > Geographic and Overlay area codes • 7 vs. 10 digit dialing > Toll free increase (888, 877 etc. ) > Depletion of number inventory • Explosion of cell phones, pagers, fax machines, 2 nd lines • Recovery program underway (000’s block pooling) > Local Number Portability • Support of a competitive marketplace 27

Signaling > The method of controlling the routing of a call • Uses in-band tones and computer communications > Dual Tone Multifrequency (DTMF) i. e. Touch. Tone® in-band signaling > SS 7 (Signaling System 7) (out of band) • Very fast and reliable • Sets up calls via Signal Transfer Points • Performs special data retrieval SCP STP From service Control Points • 800 number translation > Call Progress Tones • Busy (60 IPM) • Reorder (120 IPM) • Special Information Tones (SIT) > Vo. IP essentially uses in-band signaling • Security and reliability issue 28 Central Office

Old-Fashioned long distance 1 2 AT&T Long Lines . . . 1 2 2 . . . 2 3 End Offices 29 5 3 3 . . . 3 4 Tandem Offices . . . 4 4 . . . 5 5 . . . 5

Modern long distance > The network is “flatter”, with multiple LD Carriers > The Local Access and Transport Area defines a Bell Company’s operating area. > Rural telephone companies may connect directly to LD carriers but often connect to the closest Bell tandem switch LATA 5 4 5 AT&T . . . 5 MCI : Sprint 30 LATA 4 5 . . . 5

Operator Services > Human intervention assists in call processing • • • Collect calls Bill to 3 rd party International calling assistance Directory Assistance Emergency call transfer > Dial “O” for local operators TOPS* Tandem End Office > Dial “OO” for LD operators * TOPS – Traffic Operator Position System – a Nortel product 31

Let’s talk Wireless!!!! > Wireless communications are booming > Most of the world utilizes the GSM radio format > In North America, multiple radio formats in use: • CDMA, GSM, AMPS, TDMA • Impacts the development of wireless devices • GSM and CDMA formats are incompatible ((( ) )) ((( Mobility Switching System Base Station Controller ) )) Cell sites Only a small portion of the call is carried over wireless 32

((( Why is it called “cellular”? > A cellular radio has limited range > As a user moves out of range, the call transfers to a different tower (a ‘handoff” that is often the source of dropped calls) > The area served by a tower is a “cell” > Cells are laid out in a honeycomb pattern and can be subdivided into new cells as traffic increases > Adjacent cells use unique frequencies to avoid interference requiring the phone to change channels > Cells can also be “sectorized” to increase capacity 33 ((( ) ))

Wireless to the world > Mobile calls are wireless only at the edge > The remainder is handled exactly like a wireline call Today’s network … : Wireless network Mobility Switching System Base Station Controller LATA 5 4 5 LD #1 . . . 5 LD #2 LD #3 34 Cell sites

Wireless Communications > More than just PCS/Cellular Service > Wireless data is becoming more and more important • • • Wi. Fi technology is spreading rapidly Spokane and Philadelphia city-wide Walla rural network (1500 square miles) Small hot spots (Mc. Donald’s, Starbucks) Home networking > Wi. Max will emerge to compete with Wi. Fi • More than just range extension • Adds Quality of Service (Qo. S) assurance • Terminal pricing will be critical > Security is an issue – war chalking Convergence of wired and wireless on an IP network is the future! 35

What is the Internet? > The Internet is a large computer network • Originally designed to allow communications in times of nuclear war – DARPA design • Largely a self-healing network > All data transmission is packetized • Utilizes IP (Internet Protocol) routing • Packets are switched by routers > The most popular applications are: • Email • The World Wide Web • Access the web using Modems, LANs, x. DSL, cable etc. • Web content is stored in servers at web sites 36

What is IP? • Internet Protocol is the grammar of the Internet • A standard method of computer communication • Utilizes a unique 4 -byte addressing scheme (e. g. 47. 11. 97. 255) • Sends variable length packets • Packets are delivered on a “best efforts” basis • Packets are often lost • Packet delivery times are relatively slow and quite variable • Error detection and correction are the responsibility of end users • TCP (Transmission Control Protocol) does this • Error correction is accomplished by retransmitting missing or damaged packets • Real-time applications typically do not correct errors 37

The Internet’s dirty little secrets > The Internet was never designed as a real-time delivery system. • The transit time for individual packets can vary substantially • This variance is called jitter and effectively adds delay to realtime applications – e. g. VOICE > Traffic capacity is relatively poorly engineered, particularly at the edges • IP doesn’t handle congestion well • Delay increases the jitter limits • IP will drop packets under congested conditions Delay and packet loss are the two major causes of voice quality deterioration in Vo. IP calls 38

Packetizing voice (Vo. IP) > The format for carrying voice is changing to a packetized format, primarily using IP • Voice can be transmitted much like data is over the Internet > Maintaining voice quality is a big issue • Control of delay is essential • Packet loss must be minimized • Compression has some disadvantages > “Voice over packet” and “Voice over the Internet” are not exactly the same > Traditional TDM voice will be around for years > Interworking of Vo. IP and TDM is mandatory 39

The role of Vo. IP > Vo. IP is many things to many people > To the Enterprise: • A vehicle for major expense reduction • A key to improving productivity through feature integration > To the Carrier: • A vehicle to lower LD costs, enhance CLEC reach and build unique customer networks • Eventually, the means to operate one network, eliminating TDM > To the Consumer: • Today, primarily a method of buying cheaper telephone service It will take many years for Vo. IP to totally replace TDM; but high value subscribers will adopt the technology sooner. 40

How does IP telephony work? (IP in the middle) SS 7 Gateway “Gatekeeper” IP TDM Gateway PSTN Local Exchange New York PSTN Local Exchange Legend SS 7 Protocol Bearer Path Interworking Protocol IP Control Protocol 41 Paris

How does IP telephony work? (Totally IP) SS 7 Gateway Telco provides the link to the Internet “Gatekeeper” Telco provides the link to the Internet IP TDM PSTN Local Exchange 42 PSTN Local Exchange Gateway DSL over existing copper loops Vo. IP line TDM Legend SS 7 Protocol Bearer Path Interworking Protocol IP Control Protocol DSL over existing copper loops Vo. IP line

How does IP telephony work? (IP to PSTN) SS 7 Gateway Telco provides the link to the Internet “Gatekeeper” Sydney “Gatekeeper” Telephone company terminates the call IP TDM PSTN Local Exchange 43 Gateway Common Transport Vo. IP line TDM PSTN Local Exchange Legend SS 7 Protocol Bearer Path Interworking Protocol IP Control Protocol Vo. IP line

An architecture for evolution ((( Application Server ) )) ((( ) )) SIP TA IP RTP/IP Hybrid Switch IP Gateway IP DSL TCP/IP BB DLC Analog Voice PSTN Legacy lines Eventually the hybrid becomes a softswitch. 44

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